For many people, allergies are simply annoying. They cause occasional discomfort due to symptoms such as stuffy nose or irritated eyes. Some allergies are seasonal, coming and going with changing pollen counts. Other allergies and their symptoms may persist throughout the year. Allergies occur when the immune system overreacts to an otherwise harmless substance. This hypersensitivity reaction causes an inflammatory response, which results in symptoms that are annoying but not particularly serious.
But some allergic reactions are far more serious. For a minority of people with severe allergies, exposure to a particular allergen can be a life-threatening experience. For example, a bee sting is briefly unpleasant for most people. After some initial pain, there’s usually some minor swelling or redness, which subsides within a few hours.
For reasons that are not entirely clear, though, some people become dangerously sensitized to particular allergens. When certain people are exposed to their trigger—say, a bee sting—it can quickly cause a life-threatening reaction called anaphylaxis. Their immune system overreacts to proteins in bee venom, resulting in dangerous symptoms that require immediate medical attention.
Testing for Severe Allergies
If you suspect you may be severely allergic to something—whether it’s a particular food or some other trigger—it’s important to get tested. Testing can take several forms. Your doctor may order a blood test, or one of several types of skin tests. In either case, results will be evaluated in light of your specific patient history. Allergy testing should be performed. The results should be interpreted by experienced healthcare professionals.
It’s possible to develop an allergy to virtually any form of protein, but the great majority of food allergies are caused by just a handful of foods. These trigger foods include milk, soy, eggs, wheat, peanuts, tree nuts, fish, and shellfish. Other common allergens include bee or wasp venom, and certain medications such as penicillin, an antibiotic.
IgE Skin Tests
There are basically two ways to test for allergies. One involves applying the suspected allergen to the skin, while the other involves drawing blood and looking for specific antibodies in the blood.
The Skin Prick Test
Skin testing is the most common form of allergy testing. It can be done fairly quickly in most cases. In a clinic or doctor’s office, a healthcare professional will apply small amounts of potential allergens directly to the skin. This is usually done on the forearm. The skin is then pricked at application sites in order to introduce a small amount of the diluted allergen beneath the surface of the skin. This is called the skin prick test. A raised welt will form at the site of the skin prick if you are allergic. Within about 20 minutes the allergist will be able to tell if you are allergic to a given substance. If not, the skin will remain normal. The test takes a scattershot approach to identifying potential allergens; it tests for reactions to numerous different substances at one time.
A second form of testing is called intradermal testing. In this variation, a small amount of diluted allergen is injected directly beneath the skin with a small needle. This test is most often used when a specific allergen is suspected. After the skin prick test or intradermal testing, the patient must wait 20 minutes or more while the allergist monitors for any signs of reactivity. In rare instances, a patient might have a serious allergic reaction, so careful monitoring is important.
The Patch Test
A third variation, called the patch test, involves the application of a solution of dilute allergen to the skin on a fabric patch. The patch is taped to the site (a forearm, or even the back) and is left in place for about two days. Results are read within three days.
Blood testing is another option. A small amount of blood is drawn from the arm. It is then tested in a laboratory for the presence of specific antibodies to allergens. These antibodies are called IgE antibodies. Testing for the presence of specific antibodies is done using a method called enzyme-linked immunosorbent assay (ELISA). An older method, called the radioallergosorbent test (RAST), is seldom used these days. Unlike skin testing, blood testing can yield accurate results even if you are taking allergy medicines that may suppress skin reactivity. The downside is that it may take longer to get results.
Drug Provocation Testing (DPT)
Finally, a method of testing for allergy to specific drugs is called drug provocation testing (DPT). This is a relatively rare test, and it is somewhat controversial. Various methods exist, but most consist of exposing the patient to a small amount of a suspected drug. The test may also be called controlled challenge, reexposure, drug challenge, etc. It is generally only performed after other testing methods have indicated a possible allergic response, and only under certain specific conditions. It can help rule out misdiagnosis of drug allergy.